The present invention relates generally to a method of repairing cracks in a stationary airfoil or vane of a gas turbine engine by microwave brazing.
A gas turbine engine includes stationary airfoils or vanes made of a base metal of either cobalt or nickel superalloy. The vanes may crack due to high temperature thermal mechanical fatigue and hot corrosion that occurs during engine operation. The crack is usually repaired by brazing. A braze alloy including approximately 50% of a base material and approximately 50% of a braze material is applied to the crack. The melting temperature of the braze material is lower than the melting temperature of the base material.
After the braze alloy is applied to the crack, the vane is heated in a heating furnace. The braze alloy melts and fills the crack. Typically, the vane is heated for approximately 6 to 8 hours to melt the braze alloy and repair the crack.
The percentage of the base material should be relatively high and the percentage of the braze material should be relatively low to prevent the braze material from saturating the braze alloy and to ensure that the composition of the braze alloy is as similar as possible to the composition of the base metal. However, as the percentage of the base material increases, the melting temperature of the braze alloy also increases. If the vane is exposed to higher temperatures, the vane can possibly distort and lose its properties. Therefore, the braze alloy generally includes a high percentage of the braze material to keep the melting temperature low.
Hence, there is a need in the art for a method of repairing a crack in a vane of a gas turbine engine that is fast and that overcomes the shortcomings and drawbacks of the prior art.